The invention relates to a process for aerating suspensions, particularly to flotate them, for example in deinking of pulp suspensions, with one or more stages and/or cells, where each stage/cell has its own separate liquid loop. In addition, the invention relates to a device for implementing the process.
A process of this type is known, for example, from EP 1 124 001 A2, where the individual flotation stages can also be designed according to U.S. Pat. No. 4,255,262, EP 0 243 690, DE 31 20 202, or U.S. Pat. No. 6,208,549, for example.
Processes of this type are used to remove impurities and printing ink particles from pulp suspensions, particularly those produced in waste paper treatment. By applying this type of process, non-specific removal of mineral components (e.g., fillers containing ash, etc.) is achieved because their chemical surface properties (particularly loading) are such that they react differently from the ink particles, which are relatively easy to render hydrophobic, in the pulp suspension. In addition, the specific weight of the mineral components is approximately two to three times higher than that of the ink particles. In the processes known, however, some disadvantages occur in selective flotation. If, for example, attempts are made to target the removal of fillers by making certain changes to the process, this always results in a drop in the efficiency of printing ink removal, which leads to a need for additional changes in gas loading, adjustments to the raw material fluctuations, and changes in throughput. Furthermore, if the overflow quantity is increased in order to raise the removal rate of mineral substances, the fibre loss rises in equal proportion to this, which leads to greater expense for disposal and raw materials required.